In Defense of the Passive House Standard

A point-by-point clarification of why the Passive House Standard sets a worthy goal for North America

Marc Rosenbaum (left) is the founder of Energysmiths in Meriden, N.H. He is a designer and engineer specializing in low-energy-use buildings. David White (right) operates Right Environments in Brooklyn, N.Y. He provides consulting services on Passive House principles to architects and teaches courses on Passive House Planning Package software.Image Credit: Marc Rosenbaum and David White

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We recently read John Straube’s paper, “Comparing Passivhaus Standard Homes to Other Low-Energy Homes,” comparing the Passive House (PH) standard with the Building Science Corporation (BSC) cold-climate approach. After a careful reading we find that the conclusions reached are based on some significant misunderstandings about the Passive House standard. In this paper we will note these misunderstandings, page by page, and will compare the heating energy requirements and total primary energy requirements of the BSC example house (as given in Insight #25) with the PH standard applied to the same house.

Our intention in writing this article is to further the inquiry into Passive House and its application potential in North America. We have both spent a great deal of time investigating Passive House over the past few years, and draw on our own personal experiences to offer to the collective inquiry what we feel to be reliable information.

The Same Energy Budget In All Climate Zones

BSC alleges that PH has “a complete disregard for climate zone in its recommendations.” It is more accurate to say that its maximum energy use targets are the same in all climate zones, which necessitates more stringent design as the climate gets colder. This prescription may indeed bear some examination, yet it’s not clear that it is less arbitrary than the BSC “5-10-20-40-60” approach described on Page Four. Passivhaus Institut in Germany is considering how the 15 kWh/m2/year space conditioning targets might be altered for extreme climates. Ultimately this discussion will include a deeper examination of what our per capita resource budget should be. Should people in colder climates use more energy in their homes than people in warmer climates, or should everyone have a budget no matter where they live?

In almost all cases Passive Houses do have heating systems. Passive solar design principles are not mandatory, as BSC correctly states, yet it is very difficult in cold climates for a single-family house to meet the standard without good orientation and locating most of the glazing on the south side. The Passive House Planning Package software (PHPP) does an excellent job of showing the energy balance through all the glazing by orientation, as well as clearly showing the losses separately from the gains. The results from design changes can be seen clearly and instantly and make the PHPP a powerful teaching tool even for experienced designers.

Delivering Heat With the Ventilation System is Not Required

BSC has the primary requirements of the PH standard correct, but misinterprets Dr. Wolfgang Feist’s comment:

“As long as you build a house in a way that you can use the heat-recovery ventilation system — a system that you need anyway for indoor air requirements — to provide the heat and cooling, it can be considered a Passivhaus. Since you need a house to be tight, you need a supply of fresh air. If you need that anyhow, the idea is to do everything else — the heating and cooling and dehumidification — with the ventilation system.”

BSC takes this statement for its converse, that any heating and cooling system that also provides ventilation (presumably as a portion of its total air flow) makes a Passive House. The rationale of the fresh air heating system is that such a small system has a very low incremental cost, after taking mechanical ventilation as a given, compared to a conventional German hot-water radiator system. Radiator systems are less common in the U.S., and how the mechanical-envelope cost tradeoff game is played here is a very interesting question to us. But it’s worth noting that due to excellent window surface temperatures, the heating can be delivered at any point in the room, minimizing duct runs. Further, were heating/cooling equipment mass-produced for this purpose, it ought to be less expensive than conventional equipment.

PH standard agrees with BSC that delivering all the heating with the ventilation system may be overly restrictive, so this is not a requirement. Some use supplementary electric heat, while others use recirculating forced air systems. However, the peak load may not be as restrictive as it seems. Due to superlative envelope design, even light-construction passive houses experience negligible drops in temperature during unmet load hours. For this reason peak loads are calculated over a full 24-hour cycle, which means not only a less severe outdoor temperature, but also the use of that day’s internal and solar gains to offset the load. This makes a big difference. For a current project in Syracuse, the 24-hour average temperature, used in place of ASHRAE 99.6% temperature, results in a 15% peak load reduction. Combining this with useful internal and solar gains leads to a total reduction of 38%.

Secondary requirements include maximum window U-values and minimum heat recovery efficiency. Both of these requirements have been relaxed somewhat in North America due to the scarcity of products that meet these requirements. We suggest that a key contribution of the PH standard in Germany is the market stimulation for dozens of innovative products – including low U-value, airtight windows and doors; very efficient HRVs/ERVs; combination mechanical systems; home run small diameter flexible duct work; excellent air tightness products; and more – to serve the demand created by the PH standard. It’s worth noting that the PH standard for efficient ventilation includes both thermal and electrical efficiency, and only one product in North America meets these standards.

The most significant BSC misunderstanding of the PH standard for the purposes of comparing PHs to US houses is the PH method for calculating floor area. It uses a German standard procedure for “Treated Floor Area.” It’s the area inside the exterior walls, less interior walls and staircases as well as columns over a certain size; and also less 40% for secondary spaces such as storage, mechanical rooms and basements. In the case that BSC references, a raised ranch, we believe that PH would count all the finished conditioned basement area at 100% since it would have normal light and ventilation, but mechanical and storage spaces would be counted at 60%. The result is that the BSC 25 x 40 raised ranch would likely count at about 1,600 sf instead of the 2,000 sf that is based on exterior dimensions. This will be significant in the following comparison, as we compare the total energy of the BSC house (by BSC’s own estimate) with its requisite performance to meet PH standard.

Passive House originates in a specific heating energy demand reduction strategy aimed at cost effectiveness, and the Passive House Planning Package software reflects that. However, PHPP calculates cooling loads as well, and has a useful feature which informs the modeler what percentage of the time the building will overheat in the absence of any mechanical cooling. There are sophisticated natural ventilation worksheets in PHPP and detailed shading analysis which help the designer to minimize the cooling load before mechanical cooling is applied. Similarly, there are detailed worksheets to analyze lighting, appliance, and mechanical parasitic loads.

BSC is correct that PH includes the analysis of thermal bridges. This is because the measured energy use of the early PH’s exceeded the modeled energy use, and the PH scientists learned that bridging – in a truly superior envelope – can result in significantly higher conduction loss percentages than in a typical building. Although 2D heat transfer analysis is often done in the US, we think that the formalization of thermal bridging calculation into the PHPP and the extensive cataloging of thermal bridging coefficients for construction details is another PH contribution to North American designers’ understanding of how energy moves in buildings.

BSC re-states the 0.6 ACH50 air tightness requirement, and says that this results in designers having to choose simpler shapes. We ask, why should building form not contend with environmental performance? Tightly massed, simple shapes were the norm in cold climates until the advent of cheap non-renewable energy. Cost effectiveness is the principal mantra of the US building industry, and cost effectiveness begins with minimizing surface area of a building, so the owner buys less wall, roof, and foundation for the usable floor area gained. PH doesn’t require any particular design type, but by basing the maximum space conditioning energy consumption on usable floor area it forces designs with more surface area to work harder to achieve the standard. That’s a good strategy – prescriptive standards such as BSC’s 5-10-20-40-60 rules of thumb, or ASHRAE 90.1, or most energy codes, don’t take into account design as the greatest driver of how much energy a building uses. PH does – it’s a performance standard rather than a prescriptive one. “Green” designers are clamoring for formal expressions of sustainability, and all too often expressing in ways that are useless or counterproductive, consequently leaning more heavily on mechanical solutions and setting bad examples for others. PHPP offers them a way to make forms that work.

The BSC discussion on airtightness states that the PH standard of 0.6 ACH50 is too difficult to achieve for production builders. In Germany and Austria, this has proven to be untrue. Are they better builders than we are? One very experienced PH architect told us that the problem with German builders regarding air tightness is that each of them carries a knife, “…and so they are happy, but not we.” He then went on to show us air tightness products that evade the knife. We don’t expect their builders are better than ours, but we need to support the North American builders with products and methods to achieve these targets.

It is true that the incremental energy benefit of the air tightness target is very small, even by PH standard. We agree that the air tightness requirement may be separately specified because of a concern over durability of superinsulated envelopes. One of the authors was also given the following explanation by an experienced PH planner: in a Passive House, the use of a low velocity, high-temperature forced air system, with delivery not infrequently at ceiling level, means that the ability of the heating system to mix the air is very poor. For this reason even a small amount of infiltration can be a comfort problem, as cold air collects at floor level.

Dual core HRVs are not used in Europe to reach the required high efficiencies; they usually require more electrical power due to higher pressure drop. Rather, counterflow heat exchangers are common, and were available in North America years ago but have virtually disappeared from the market. Again, we need, here in North America, the innovative products PH has spawned.

ASHRAE 62.2 Assumes That Envelopes Leak

BSC is correct that the NFRC rating method for window U-value leads to higher values than the European convention. It is also true that the quality of windows needed for achieving PH performance in cold climates is difficult to find on the North American market, certainly from the major manufacturers, and this has been recognized by builders of low-energy-use houses in cold climates here for three decades (in the late 1970s one of the authors built windows for his own house with 4 to 6 layers of optically clear 4 mil polyester between two layers of clear glass â˜º.) U.S. windows have a long way to go even to achieve parity with what is currently available in Europe. As California (and the rest of the US as a result) did with refrigerator efficiency, we need a government mandate with minimum window performance to raise the bar for everyone and bring much better windows to the market with a small increase in cost (the real price of refrigerators has dropped since 1970, although energy efficiency has improved by factor 4). PH arrived at maximum window U-value requirements from the consideration of human comfort and radiant heat exchange, not principally from energy requirements, and this is more challenging in cold climates. Right now we can’t meet the PH recommendation for interior surface temperature in cold climates with windows available here.

The discussion in the BSC paper on over-ventilation and its energy penalties lacks key information: ASHRAE 62.2 explicitly assumes 0.02 cfm/sf of infiltration as a component of the total air change in the building. BSC’s 50 cfm of ventilation for the 2,000 sf, three bedroom house is added to 40 cfm of assumed air leakage, resulting in a 90 cfm ASHRAE expectation in this house. The PH requirement for this house is about 80 cfm, with much less infiltration – about 10 cfm seasonal average– so the total is close to ASHRAE 62.2. Thus PH ventilation is not tantamount to using a mechanical ventilation system to impose air leakage, but rather diverts the typical leakage through the mechanical ventilation system, so that it can serve both heat recovery and space heating. IAQ is also improved – as we all agree, cracks are of questionable cleanliness.

PHPP does warn against overventilation leading to overly dry air (at around 110 cfm for this house). To our knowledge, ventilation rate is not increased to deliver heat in cold climates.

At this point we begin to inform the numerical discussion using the calculation of Treated Floor Area. To provide a peak load of 10 W/m2 of TFA for the 2,000 sf home would require only 81 cfm (68°F room, 126°F air, 1600 sf TFA), not 115. And as we demonstrate above, this is a good ventilation rate by ASHRAE standards for a house with PH air tightness. This means that a fresh air heating system provides about 30% less power than BSC supposes; but as noted above, the peak load could be almost 40% lower than BSC supposes.

Passive Houses Can Have Hydronic or Forced-Air Heating Systems

In our experience, many PH have been built with conventional hydronic and forced air heating systems. It is worth noting that in very low-load buildings the radiant floor will not be perceived as being warm (2°F above air temp at peak load) unless it’s concentrated in a small area like a bathroom. Recirculating air systems are common in the authors’ current PH work, yet they are much smaller than American systems – around 0.15 cfm/sf. This is not only because the envelope and ventilation heat losses are minimized – it’s because those envelopes justify a paradigm shift in peak load calculation, as noted above. The ductwork is still ventilation scale, and there is substantial capital savings in equipment size (even for single family homes), perhaps more as some of the German modular systems make their way to North America.

While durability and air quality may not be explicit in the text of the PHPP, they are both of paramount importance to the community that developed and implements PH in Europe, as they are to all of us. Some are implicitly addressed in the PHPP, for instance in the air tightness standard and the ventilation guidelines.

The BSC Design Uses 365 More Therms Per Year

The BSC paper concludes with a comparison of a BSC 5-10-20-40-60 house and a PH. We use BSC numbers here, the correct numbers for a PH, and matching conversion efficiencies for mechanical systems. Starting with heating, BSC gives the 2,000 sf house a heating load of 12,500 kWh/yr, which is served by a natural gas furnace at 96% efficiency, so the energy usage is 13,021 kWh annually. Our understanding is that BSC houses can achieve better performance than this, so note that this number may be high. PHPP converts this to primary energy with a factor of 1.05 (recognizing that it takes energy to deliver the gas to the house) so the primary energy for heating is 13,672 kWh.

The PH would have a Treated Floor Area of 1,594 sf – which is 148 m2 (see TFA calculation above). Its maximum allowed heating load would be 148 m2 x 15 kWh/m2/year, or 2,220 kWh. With the same gas efficiency and primary energy conversion, this is 2,428 kWh/year of primary energy.

BSC adds 4,000 kWh of gas at 92% efficiency for DHW, resulting in 4,565 kWh/year of primary energy, and 4,000 kWh of electricity for lights, appliances, and mechanical parasitics, with a primary energy factor of 3.0, resulting in 12,000 kWh/yr in primary energy. Total primary energy for the BSC house is 30,237 kWh/year – for the PH it is 18,928 kWh/year. Per square meter TFA the figures are 204 kWh/m2yr for the BSC house and 128 kWh/m2yr for the PH. So the PH doesn’t quite make it either (maximum primary energy must be below 120 kWh/m2/yr), although PHPP assumptions for electricity PE factor, DHW usage, plug loads, etc. would in fact make it certifiable (another discussion).

Recognizing that the DHW and electricity in this comparison have been the same in both houses, let’s focus on the difference in heating energy. The difference in fuel consumption is 365 therms/year. Is this a trivial quantity? We don’t think so. Using BSC’s approach of making up the primary energy difference with PV, it would require about 3 kW of PV to offset the 11,244 kWh/yr of additional primary energy required for heating. At $8,000/kWp installed, this is $24,000. Is this less costly than spending the money to upgrade the BSC house – already quite good – to PH standards? We think not. Also note that PV is very energy-and-materials intensive to make, and is for the former reason assigned a PE factor of its own in PHPP calculations. Further, the extra insulation and air tightness of the PH won’t wear out (one author was an early adopter of grid-tied PV – his first inverter has long since bit the dust), are most economically provided during initial construction (while PV can wait), and guarantee survivable conditions during an extended fuel outage. These may be reasons that the heating energy demand target stands separately from the primary energy target in the Passive House standard.

BSC goes on to assume the levels of improvement that would be required to bring the BSC house to PH levels. It is not necessary to cut the losses in half to cut the heating demand in half. The gains – solar and internal – remain more or less constant, so the net is reduced by half long before the R values are doubled. This is a point of leverage for the method – a typical Passive House has around 30-50 kWh/m2a of losses, with the gap to 15 kWh filled by solar and internal gains.

The R-values needed to meet the PH standard depend on the location of the house. A superinsulated house modeled on PHPP for Burlington Vt will use double the heating energy of the same house in Boston, because Burlington is 40% colder and has slightly lower wintertime solar gains. This suggests that a prescriptive rule of thumb such as the BSC 5-10-20-40-60 will result in substantially different energy consumption when used over multiple climate zones. We’d like to see some flexibility in the PH standard for climate, and also an approach that makes achieving the standard with smaller houses no harder, or even easier, than for larger ones, but we like the defined target aspect of PH, which sets it apart from all North American approaches we are aware of.

Idiots and Maniacs

BSC concludes that PH is too restrictive architecturally, more expensive, and not significantly more efficient than the BSC approach. We think that European experience belies all three claims. There is much discussion in our community about the PH standard that is not fully informed. We suggest that studying Passive House and the PHPP is time well spent, both to understand the experience and insight that has gone into the PH standard, and to sharpen one’s understanding of energy flows in very low energy use buildings. The information regarding peak loads and useful gains mentioned in this article alone could inform the BSC house – it may be closer to cost effectiveness thresholds than thought.

George Carlin said, “Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac?” Well, that might be a maniac we see hurtling down the road, but the fact that he’s still going begs the question, how much faster can we go without getting pulled over? The nature of the climate challenge asks us to reduce the energy used in buildings as quickly as possible. We’ll progress fastest if we share our knowledge and experience without attachment to any one particular way of doing things.

39 Comments

clarification?
Interesting stuff -- I love a good BS (building science) debate. But I'm wondering a little about some of the numbers here -- probably not a surprise...

You compare the PH house with a supposed 2,428 kwh of primary heating energy to the BSC design at an estimated 13,672 kwh.. It appears that no actual analysis of a specific home has gone into either of these numbers. The BSC number, you agree, seems kind of high for the specifications listed. The PH number is simply assuming that the home actually meets the PH standards. You later say how you don't think the difference in construction would be as costly as a PV system to make up the difference. This all just seems like a lot of speculation.

Can you provide any specific list of differences between the stated BSC design and the PH design that would account for the 82% reduction in heating load? I don't think changing to super windows, 0.6 ACH60 vs. 3 ACH50 and a better HRV will come close to this difference in loads.

It would be much more convincing and helpful if you had a model of the BSC design home with a projected heating load and then showed the design changes and approximate costs of a PH version of the same basic home. I'd be curious to see what sort of projected load reduction the design differences would make and how much they'd cost. I'd be even more impressed if there were some actual homes with actual energy usage data to show these differences, but I'm not so naive as to expect that ;}

I agree that modeling is
I agree that modeling is useful tool for the designer and homeowner and phpp is one option for modeling. The debate goes around and around and it seems like this is just posturing yet we all likely have the same mission of building highly efficient, cost effective homes. I guess I would need to ask: What are our collective energy reduction goals (or energy needs) to meet our climate needs? It's obviously a social problem and an overpopulation problem we have.. when you have 6 billion people on this planet all wanting what you and I have. And this is where PH is very noble in maintaining these lofty goals/ideals if we are to achieve the necessary reductions in ghg emissions.
I would also like to see what the real historical usage data between the PH and BSC of all of the homes built in the US (not europe).
Also, there is a big difference in building materials used from here to there. Another big difference, if I remember correctly, is that the HDD in Germany are fairly mild (4-5k) vs up here in Wisconsin where it can hit 10,000. And this is an issue I've had since I started understanding phpp. To be honest, the only way that I can sell the phpp to a client is if they have the same ideals and even then it's a tough sell. Speaking of clients, one of mine will be at the phpp conference (Sonya Newenhouse) see if you can sell her, I'll do the testing and building- you do the phpp.
The other thing is that to learn how to use the phpp you have to be as smart as Mark and David...and I can't say that I'll get there in this life.

Glad you've joined the discussion. We just took the heating number that John presented in his paper and didn't quibble with it. The PH number is assuming the house meets the PH std. John's house is a hypothetical house. I have looked at a small cape in the Boston climate in PHPP and the house with the basement inside the heated space the following specs meet the heating criterion in PHPP:
Wall R-50, roof R-63, basement wall R-39, basement slab R-46, windows FG frames triple glazed with two hard coat low-e layers, window location weighted to the south, 0.6 ACH50, 83% efficient HRV with very short ductwork on the cold side, one flat plate collector for DHW needed to make the PE criterion. I don't know if John's theoretical raised ranch would need higher or lower numbers - it's larger, which is usually a benefit.

There is a lot of measured data on PHs in across Europe - not just in Germany. The Smith House and the Fairview House have been well-monitored in the US and there are no reasons to suspect that these houses will not perform on this continent as they have in Europe. There is real data on these houses, Michael - no one has accused the Germans of being sloppy in their data collection :-) It worth noting that the houses being built in Urbana by Klingenberg and Kernagis are affordable housing, so the standard doesn't automatically mean expensive. Their prefab 14" I joist walls with blown-in fiberglass don't seem to be unreasonable in cost for the close to R-60 they provide.

At the just-concluded PH conference in Champaign, the keynote speaker Gunter Lang from Austria showed an immense range of buildings meeting the PH standard, and told us that 1 in 4 new housing units in Austria are being built to this standard. As we have stated, we have some aspects of the PH standard we'd like to see evolve in the US, but overall we are convinced that we need to aim higher than what is being done here. The Swedish definition of a PH is somewhat different from the German standard, with the targets based on climate zone and house size (it's a simple 2 x 2 matrix - the US is much more complex.) We appreciate that evolution of the standard and we also appreciate the stringent and defined target as a response to climate change. As a final point of interest, the Swedish standard doesn't allow fossil fuels, an indication of their seriousness (and perhaps also of their rich forestry and hydro resources...)

thanks for the reply...
I think it's great that there are people building homes to PH specs and think we can learn a lot about high performance homes from what the PH people are doing. But I still don't see any solid case for PH over the BSC specs. How much annual savings do you get from an R-46 slab? What are the extra savings vs. costs for the R-50 wall vs. than R-40 wall? I think these are still open questions and I also think the answer will vary depending on climate, construction costs, and other factors.

Have you tried using PHPP on the same house design but with BSC specs to see what the projected energy usage would increase to? If you could combine that info with an analysis of the estimated cost differences of the designs then it might provide some useful place to start the comparisons. Of course, it would still be based on projections from the software. Much better would be real world results from large groups of homes.

I don't read German and I have yet to see any large scale analysis of single family homes built to PH standards. Can you provide a link to any source of actual energy usage data for a reasonable number of PH homes? The few reports that I have read make various adjustments to the numbers and haven't provided me with the type of data I'd like to see to really understand what they've found. I'm not saying I don't believe that the homes may perform as they should on average, it's just I haven't seen much data on that and I have heard some people make modeling accuracy claims that I don't think are realistic.

I do like the idea of having the PH energy usage standard vary with climate, which it sounds like the Swedes have done. I also think it is not a good idea to create usage thresholds that scale proportional to floor area, unless you like penalizing small houses. .

Some of the developments do better than others, some are off by a lot. At the time this study was done it was very early in the process and the technology was still fairly new. One development deserves to be highlighted and that is the Hanover Kronsberg project. Measured results here meet the predicted results almost exactly.

By my calculations of the BA BSC house compared to PH , if additional measures are taken to bring DHW and household down further to typical PH consumption, then the PH project saves 43% primary energy over the BA case and the site energy consumed is less than half of what the BA BSC home consumes. That is significant.

If anyone among you has used PHPP extensively, surely you've noticed by now that a given house to typical Passivhaus standards (if it has a good passive solar irientation) needs *less* heat in many a North American climate than in northern Europe? (Assuming the same level of internal heat gains).

Much of the northern USA is at latitude 40-45 deg N and it receives considerably more winter insolation than northern Europe gets. The UK is at 50-60 deg N and as you may know is often covered in cloud from the nearby Atlantic Ocean. Germany and the Low Countries aren't much further south.

Obviously, if the outside temperatures are more extreme, I agree that a building in North America would tend to have a higher peak heat demand than it would in the UK or Germany.

Thanks Katrin..
I was already aware of the report you linked and am a little surprised that there isn't something more recent and focused on single family detached homes -- which is what we are mostly talking about here. The report only includes individual results for two detached single family homes. In one home, the measured heating energy usage is 69% larger than the software projection and in the other home it was 79% larger than the projection. The actual heating consumption for the two homes averaged more than double the 15 kWh/m2/yr threshold.

Looking at the data for all 11 projects in the report, the actual heating usage averaged 33% more than the projected usage..

The results for the Hanover Kronsberg project are for attached homes with district heating and have the sort of issues and adjustments that I referred to previously that it make it harder to assess things unambiguously. Some issues included unoccupied units that were left heated, adjustments for district heating system distribution losses within the units prior to the Btu meter, adjustments for indoor temperature, etc.. In terms of the primary energy threshold, the district heating was counted as a 0.7 source/site conversion -- giving credit for cogenerated electricity. Each of these issues/adjustments may be sound but it does make things a little less clear. The bigger issue is that it should be far easier to meet the heating usage goal in attached housing.

I was hoping there might be a dataset with dozens or even hundreds of PH single family detached homes with measured and projected energy usage data.

I'm also curious about your calculation about a PH home using 43% less energy than a BSC home. Is that based on modeling some specific project and then changing the specs between the two standards?

This is a good question if
This is a good question if there has been a more recent published study focusing on single family detached measured PH performance in Europe. I am currently not aware of it and will certainly check into that.

I agree with you, the issue is rather complex and it is difficult to arrive at a clear picture as there are so many variables.

You are absolutely correct that just simply taking the BA home and adjusting for different modeling parameters, i.e. treated floor area discrepancy, does not result in an accurate assessment. That is why, in my initial response to John's article on our bulletin board, I used his specifications and input them in the PHPP file for a PH home that we have realized here in Urbana. I assumed his wall R-values, airtightness, ventilation rate and mechanical lay out. That comparison came out to a difference of over 30% for primary energy, higher for site energy.

It is in my opinion a rather mute point to keep this discussion in the % realm. To really see we will have to do the work and model two homes, one with BA and one with PH specs in the same modeling tool. Now, here it would then also be interesting to model both in PHPP and both in another program and compare the results and do an analysis (I am assuming that the results will differ from tool to tool) which tool recognizes what factors and which might be blind to others and how that effects the overall result.

My over 30% result for BA home in PHPP is based on climate zone 5 (Urbana, IL). As we do the same exercise in climate zone 6, the PH home adjusts its envelope and maintains the same energy consumption, the BA home is maintaining the same envelope specs and therefore will use more energy compared to the PH home. So, as we move north, the over 30% increase in primary energy consumption will make the comparison worse for the BA home.

The 43% was a result of a calculation for which I simply took the same table that John provided in his paper and I calculated the new heating energy demand for a Passive House. I took a different approach than Marc and David. Instead of adjusting the treated floor area, I adjusted the PH energy characteristic value of 15 kWh/sqm yr to 10 kWh/sqm yr. This is the same approach that Minergie-P in Swizerland has taken. They had the same problem, they were calculating their performance goals based on exterior home dimensions. They adjusted the heating demand per sqm yr by reducing it by 30% to 10 kWh/sqm yr. If you do that for John's sample case plus reduce energy consumption of household and DHW to the levels that he proposed in his paper, than the reduction for primary is about 43% and site consumption drops to about half or more. But again, you are absolutely correct, this comparison is just an approximation and will vary by climate.

I agree, this is all pretty theoretical and the question remains, can we realistically build those single family homes and do the measured results match the predictions in the various US climate zones. Hopefully soon we will have more measuring and research results to back those claims up and/or to learn from them.

Thanks for the response...
It seems like we are all after the same thing and would like to see more measured results for all low energy designs. It is quite refreshing to hear the debate happening about whether new home envelopes should be 75% or 90% better than code rather than looking at 15% or 30%.

Information on built Passive Houses
Hello all.
Presently there is >15.000 passive Buildings built in Europe - single family homes, apartment blocks, offices, sport centers, kindergardens ,High schools etc. Maybe 10-20% of these buildings have measurement data from several years available. The driver for the development is the Passivhaus institute in Darmstadt, Germany.

At this moment many European countries are planning to set a demand for Passive house performance for new buildings in the building regulations before 2020 ( United Kingdom, Germany, Finland, The Netherlands, Ireland, France,Norway) .
Most Passive houses are built in Germany , Austria and Switzerland, and for that reason most data is in German language.
A number of databases are however also in English- and one of the largest can be seen at this link , where I did a total search of the database.( ca. 1250 buildings, searchable in english) http://www.passivhausprojekte.de/projekte.php?search=2

Existing buildings can also be renovated close to the passive house level- Here is a report from renovation of an apartment block. It is in German language, but numbers and -a lot of descriptive pictures of how the renovation is achieved makes it easily understandable fx page 128 figure 122 comparison of calculated- and measured data. http://www.passiv.de/04_pub/Literatur/PHiB/PHiB_Passivhaus_im_Bestand_Endbericht.pdf

thanks for links
But most of them are just databases of PH buildings with their construction characteristics and PHPP-projected energy usage info -- not actual usage. The one link that seemed to cover actual energy usage is one I was already familiar with and does not seem to cover single family detached homes. Maybe I need to work on my German so I can search the sources more effectively but I still don't see much evidence about real world performance against modeling results.

The claim of 3:1 variations in space heating usage is misleading at best -- the vast majority of homes are operated within a relatively narrow range of thermostat settings. It's like saying there's a 3:1 ratio in the heights of adult men -- it may technically be true but it obscures the fact that the vast majority are in a narrow range. Occupancy is certainly a factor, but has been used as a convenient scapegoat by building modelers since the dawn of time (well, the dawn of building modeling...)

small house rehab?
I own a small 1200sf single 2br 1 ba house in Pennsylvania with no insulation, roughly 50 years old. I need to decide if its better to rehab it or knock it down and rebuild. Are there studies of the effectiveness of rehabilitation vs rebuild? The 1/2 basement 1/2 crawl space + sun room on slab seems particularly challenging to rehab. Most Passivhaus designs avoid basements. Is it practical to rehab an existing sf house over an uninsulated basement to Passivhaus standards?

Correct PV Cost Accounting???
A thought that's occurred to me lately concerns the cost accounting used for comparing energy delivered by photovoltaic (PV) solar panels vs. energy saved via envelope measures. It does not seem valid to use the average electrical output of a PV system over an entire year to evaluate its efficacy for heating load offset. Indeed, the ACTUAL daily output during heating season is likely a good deal lower than yearly average, or one wouldn't have a heating season (sunlight = summer!) Put another way, if one wants 1 kWh of PV electricity during heating season, the size (and cost) of the PV system to deliver it (and, by extension, the cost per kWh of winter solar electricity) are a good deal higher than the cost of a system which delivers an AVERAGE daily output of 1 kWh over the entire year. This, I believe, is commonly overlooked, and completely relevant to any cost comparison of heating season energy reduction tactics.

It is true that a net-metered PV system may well provide a surplus of power to the grid in the summer, and that this may well be a societal "good." This "carbon trading," however, does nothing to reduce the energy consumption of the building beyond the satisfaction of the building's immediate needs - there is not "big battery" out there to store solar electricity. When the sun is down or covered with clouds, it is grid supplied power being consumed by the net-metered and non-solar house alike. A societal strategy of inefficient houses with large PV systems on them may address summer peak power problems in the grid, but does nothing for the energy demand of these houses when the sun isn't shining...

Off-grid thinking
Graham,
You are one of the few people left who analyze PV systems from an off-grid perspective. Since my own home is off-grid, I know all about the problem of balancing wintertime PV output with high winter electrical loads. But grid-connected buildings don't face the limitations of my battery-based system.

It sounds as if you are discounting the value of the grid for ideological reasons -- to undermine the net-zero-energy approach and bolster the Passivhaus approach. But the grid permits distributed energy generation, and that's a good thing. It's possible for 100% (well, 96%, anyway, to account for inverter and distribution losses) of the electricity produced by a grid-connected PV system to be used. That's good, not bad. Much of the electricity produced by a battery-based PV system like mine is wasted, because it's produced in July, when very little electricity is needed.

In any case, Graham, your refusal to acknowledge the advantages of net-metering is frankly irrelevant, because you stand almost alone in your opposition to this now-routine use of the grid. In the U.S., net-metering (and net-zero-energy calculations) are an accepted, routine fact.

In response to "thanks for the reply..." by Michael Blasnik
Hi Michael,

I appreciate your point about making a solid case for PH. I want to clarify that Marc (I think) and I share the same questions. Although we are both big fans, our interest in writing the article was less in defending Passive House (not our title - we are both so nerdy as to have forgotten to chose one) than in fostering a well informed investigation.

I think the analysis of life cycle cost depends a lot on projected energy prices. Further, in my opinion the lowest life-cycle cost is not sufficient grounds for judgement - the accounting of cost is limited to the owner; does not take such externalities as real estate damage, medical costs, agricultural losses, etc into account. I think that to compare equivalent impact versions of the BSC and PH homes, as in the BSC article, would side step these issues. PHPP assigns a PE value of 0.7 to PV (vs 2.7 for conventional electricity in Europe). I'm not sure what's appropriate for the US, but I think it would be a mistake to count it as a straight offset, as if its embodied energy were insignificant.

Agreed about penalizing small houses. PHI has avoided a per-person standard because it is considered too difficult to enforce. I think that for us to find a way to make a per-person standard in the US has great potential, in light of our monstrous homes as well as economic outlook.

I see a lot of discussion on #1 - #3 in many forums, I don't see much on #4. Largely because most folks are still working on the wood frame model, and drywall just doesn't have enough thermal mass. ICF guys get it backwards - still no significant interior thermal mass as they are using drywall .....all that great concrete just doing nothing. Take a look at SCIPs !! This is a concrete SIP panel. Shotcrete on the inside and out, its monolithic and has huge amounts of isolated interior thermal mass. Once the interior concrete wall has reached the proper temperature, it takes an enourmous amount of energy to change it. Its a thermal battery. My SCIP shop here in SC has no HVAC and remains comfortable year round in our blistering heat. I build with them for a lot of reasons...the biggest being that it is hurricane proof. But incidentally it is more energy efficient than anything I know of - including ICF, AAC block, Adobe, regular SIPs. Check us out at http://www.envirolaststructures.com (gratuitous plug, I know, but I challenge anyone to show me something more suited to Passive House construction). I can be reached at [email protected] or 803-409-8111 if anyone has questions

Marc and David
Can you
Marc and David
Can you clarify your reference to Dual core HRVs in comparison to counterflow heat exchangers? we started out a long time back with the folded foil boxes and then went to these slowly spinning dessicant wheels and then back to folded boxes. Is there something new that I need to find out about?
Thanks for the discussion, even though most of it is over my head.
Michael

I'm not 100% sure what the question is, but: in a counter flow heat exchanger, the two air streams run in more or less exact opposite directions. This is better for efficiency because ALL outgoing air eventually "sees" outdoor temperature just before exiting the house, and ALL incoming air "sees" indoor temperature just before entering the house. This is especially important when one is shooting for upwards of 80% efficiency.

In cross flow heat exchangers the air streams run at right angles to each other. This means that a mini-stream of exhaust air that runs along the incoming OA-side of the exchanger will give up almost 100% of its heat to very cold outdoor air, but the mini-stream running along the outgoing OA-side of the exchanger air that has already picked up a good bit of heat, and therefore it cannot give up as much heat. The dual-core cross flow exchanger improves on this by allowing the air stream to mix and then go through the same process again. But this adds more friction, more fan pressure drop. The cross flow exchangers just can't reach the same thermal efficiency and fan efficiency at the same size, especially for very high efficiencies.

I've seen it written somewhere that what I just wrote above is nonsense. But it makes sense to me; otherwise someone please show me an 80% efficient cross flow HRV (single or dual core) the moves air at less than 0.7 W/cfm. I've looked around, and can't find anything close.

Why these aren't produced in the US I can only guess is a matter of market inertia. With some government intervention we might see better products - I don't expect them to be unaffordable (although the imported products are expensive, I think that is more a reflection of the Euro and import costs - I think we could mass produce these for a lower price than the best American H/ERV's).

Energy - why make it when you can save it?
Re John Straube's piece: Apart from a number of misunderstandings, the final sentence of the essay is dangerously complacent.

JS says: "As new clean, local, and renewable energy sources come on line over the next 25 years and become more affordable than current PV prices, it is unlikely that the extreme conservation measures taken by Passiv Haus to meet the specific requirements will be considered an optimal deployment of resources for cold climate housing."

The message being that there's no need to change bad habits because we'll get abundant energy over the next 25 years. Yeah like my science teacher when I was 9 telling us that we would all be driving cheap to run nuclear powered cars when we grew up! Apart from being too late to control dangerous climate change, this strategy of depending on future cheap generation of energy is unecessary - why make energy when you can save it? Prevention is better than cure, and that is what Passivhaus is about.

"Optimal deployment"
Justin,
I'm not sure why so many Passivhaus advocates are hostile to cost-effectiveness calculations. Extreme insulation measures — the classic example we have all been discussing is 14-inch-thick sub-slab foam — are another example of waste and greed, not a good model for green construction. Why should one house on the block insist it needs 14 inches of sub-slab foam, while other houses need retrofitting? We should take no more insulation than our fair share.

Once insulation exceeds the cost of a PV array, it's a little nutty to insist on going the expensive route. We have a climate crisis, and millions of existing homes need to be fixed. Pretending that cost-effectiveness is irrelevant is an example of sticking out heads in the sand. A good engineer evaluates all available alternatives and optimizes a building's design.

Cost-effectiveness
Cost-effectiveness is a flawed, falsely rational way of thinking. For starters it attempts to reduce the value of an improvement to dollars only which forces other benefits to the sidelines. For example, in the case of upgrading windows, 'cost-effective' only measures the savings on fuel costs, while ignoring a host of benefits, such as improved thermal comfort or less condensation and mold growth.

Note that no one applies cost-effective tests to other house features besides energy measures. This creates a dichotomy in the minds of consumers that justifies spending freely on preferred amenities while limiting energy measures. And why not? Everyone agrees that cost-effective is the standard for energy investment.

Cost effective always reflects current fuel costs (or the marginal cost of the next kWh or therm). What was cost effective for attic insulation in 1978 at low electric and gas proces was R-19. Now we specify R-49 as cost effective. What happened? Only that the fuel cost went up.
Now, what do we do with all those once cost-effective R-19 attics?

Cost-effective measures will never get us the low energy use that climate change dictates we must achieve. We need to decide an energy and carbon budget for a house and let designers, builders and researchers figure out the best mix of measures to achieve the goal.

If your off-grid house were suddenly grid-tied, would you use less non-solar energy in the winter than you do now? I believe the answer is "no." It would be nice that you could "carbon trade" your excess summer power to the grid, but it would not make your house more efficient in winter, and seems to be the argument you're trying to make. Summer air conditioning is another story, because the peak demand tends to correspond more closely with PV supply.

I am not against grid-tied PV, I just think it's a lot less cost-effective than you suggest. I really only have two problems with it: night and winter.

Peak Heating Load
This is a great discussion, and greatly appreciated!

Regarding modeled performance and the selected design temperature Marc and David have said: "For this reason peak loads are calculated over a full 24-hour cycle, which means not only a less severe outdoor temperature, but also the use of that day’s internal and solar gains to offset the load."

This is troubling to me. If the PHPP modeling tool uses a dynamic model that includes solar gain and internal loads then the beneficial affect of the better performance of the PH will show up in the model output…as better performance and reduced annual energy use. But why does the PHPP use a different design temperature?

What would be much more valuable would be to use the ASHRAE or code dictated minimum temperatures to demonstrate code compliance and then use the model to show us what the annual heating profile actually looks like. Based on the profile, informed decisions could be made regarding heating equipment sizing and selection.

Can the PHPP do this for us? Why does the PHPP modeling tool need to change the input temperature data to show good performance? Any home for which heating equipment is selected and sized by using artificially high design temperatures would call for smaller heating equipment. I do not doubt that a Passive House will outperform others…but any procedure to select and size heating equipment by using unusually mild temperature data is difficult to justify.

It seems that if the PH Standard and the PHPP software are to be credible the modeled performance must be shown to be superior to other designs for any given design temperature...not for arbitrarily selected design temperatures.

Do grid-tied houses use less fossil-fuel-generated electricity?
Graham,
You asked whether my off-grid house would use less "non-solar" (that is, fossil-fuel generated) energy in the winter if it were grid-tied. The answer is clearly yes. During long cloudy spells during the winter, I currently generate electricity with an inefficient gasoline-powered Honda generator. If I were hooked up to the grid, I would have access to hydroelectricity from Quebec.

When it comes to making good use of PV-generated power, the grid is wonderfully efficient. Off-grid homes not only waste electricity during the summer -- because they generate PV electricity that no one uses -- they also waste electricity during the winter -- because they use inefficient gas-powered generators. The grid is good. PV is good. Grid-connected PV is very good.

By the way, I have plans to put up a wind turbine to lower my gasoline consumption during the winter.

There is an inlet and oulet manafold (machine fabricated) to get the right air to the right holes, so the surface area of exchange is much higher than in simple flate plate counter current heat exchangers.

You are missing my point. I am not saying that grid tied solar is a bad thing, nor that it is less efficient than off grid solar. My previous question to you was a thought experiment. Again, whether a PV system is tied to the grid or not is irrelevant to reducing the building's energy use beyond the energy use that is actually offset at the time by the PV system output. Excess PV power "banked" on summer days is a good thing for society, but it does not alter the fact that a home with a typical grid-tied PV system needs externally supplied power at night and in winter - there is no "big battery" out there, grid power used at night or in winter is largely non-renewable in most of this country. If the grid IS clean, great (and that IS the long term solution), but making the argument that "donated" excess power on summer days is equivalent to power not used in winter is misleading and incorrect. The "donated" excess power argument is no longer about energy efficiency, it's about carbon trading. If we are to talk about carbon trading, rooftop PV may not be the best option (maybe it is, but that would have to be studied.)

If we go back to the argument about energy efficiency, and costing insulation against the energy generated by a PV system, it is not valid to take a PV system's average daily output (over a year) and compare that with heating energy savings brought by insulation. To do this correctly and honestly, you would need to compare the PV system's output on a seasonally adjusted basis. If you do this you find that the winter PV power for heating is much more expensive than when the summer excess is averaged in. The range of cost effectiveness for insulation moves higher. This is ALL I've been saying from the beginning - is this still unclear?

BTW, The Passive House standard, IM(H)O correctly recognizes this, which is why PV power is not permitted as an energy consumption offset beyond what is immediately consumed. The software does "recognize" and "acknowledge" the carbon reduction brought by a PV system, but it does not call a building "efficient" based on excess energy production during part of the year. A building is called "efficient" based on the energy it actually uses...

To take this analogy further...
Would you advocate that houses closer to the city center (assuming people commute there) be less well insulated than those further out? After all, the reduced carbon emissions due to shorter commutes is a benefit. What, however, is the logical difference between allowing excess summer electrical production to justify reduced shell efficiency, but not location? The well-located house might very well have an overall lower carbon footprint. Add a vegetable garden, composting, etc., and it's really doing well - should we be okay with reduced insulation because of that? I would say not, since the efficiency of the building shell is not improved by any of these factors.

Judging others' lifestyles
Graham,
You raise interesting questions about house location, vegetable gardening and composting. If your point is that judging others' lifestyles is complicated and fraught with danger, I agree. I certainly try to avoid playing the "holier than thou" game. Clearly it's possible to live in a poorly insulated house while still having a small carbon footprint. In fact, that is typically the case in Third World countries. All of us living in high-tech, high-energy, First World countries should be contemplating exactly these questions.

You still seem hostile to the entire concept of net-zero-energy homes. I'm not sure why, but there seems little chance that you'll change your mind. For those who are still sitting on the fence, I'll state the idea behind net-zero-energy homes: the designer strives to reduce energy consumption to very low levels, through a combination of strategies including increased airtightness, increased insulation thickness, good window choice, and the selection of very efficient appliances. The remaining load -- which should be quite small -- is met with on-site renewable energy sources (usually PV). Since most homes are connected to the grid, it is assumed that the PV system is sized so that the annual electrical production of the PV system is equal to the annual electrical demand of the house.

That's not very complicated, Graham. You make it more complicated by insisting that every grid-connected house needs to have its PV system sized as if the house were off-grid. That's nonsense. Moreover, your insistence on very thick levels of insulation -- insulation that is less cost-effective than PV -- results in a waste of resources (namely, the need for very thick insulation that would be better shared with one's neighbors instead of used on one person's house).

Both right
We can agree that there must be some point where the design process turns from conservation improvements to renewable generation. We also (I think) can agree there is a point where if enough buildings are net zero then the grid stops being a good "battery" because the size it needs to be to handle winter peaks doesn't shrink below a certain amount that becomes unnecessary in the summer. So the optimum amount of insulation vs. PV will shift over time upwards, n'est-ce pas?

As Martin says, net zero buildings in our part of the world have darn good envelopes!

Cost
First off, I am a PH newbie, and I find the idea intriguing. My question is, what is the break-even point for implementing PH over a "lesser" standard?

I've read both John's document and yours. One of the big gripes in his document was how it was difficult to achieve Passivhaus standards without specialized (and expensive) components.

The most energy-efficient house may not be the most cost-efficient house if the standard is beyond the point of diminishing returns. You've load your rebuttal with specifications that I don't understand.

What I would like to see are actual dollar figures with reasonable assumption, using components that are available in the US (or, how much they would cost once shipped here from Europe). Yes, energy costs change, but put down your assumptions, and do the math, and perhaps we can plug in our own values as costs change.

In response to Mike O'Brien's objection to cost-effectiveness, we do need to keep it in mind. Higher costs often imply a higher energy input (the cost to manufacture and transport the items during the manufacturing process) and higher requirements for raw materials, which also has an ecological effect. It's not always accurate, but it is a rough way to gauge the environmental impact of going PH vs other standards. It's not very green to have to ship large housing components from Europe to achieve slightly higher efficiency if they are not available here in the US.

John says: "One Swedish prefabricated house exporter states that it does not recommend Passivhaus standards for any of its house plans other than single-storey ranches because of its experience with the difficulty of reliably meeting the stringent airtightness target with other than the simplest of building shapes."

Your rebuttal: "PH doesn’t require any particular design type, but by basing the maximum space conditioning energy consumption on usable floor area it forces designs with more surface area to work harder to achieve the standard."

My question is, how much harder do they have to work, and is it even possible? Because my guess is that only the most die-hard energy conservationists are willing to live in a box, and my wife isn't. And many people aren't. So is it feasible to meet PH standards with a non-box design, and if not, then what are the implications of being below the standards in some areas? To gain wider acceptance, PH designs have to move outside the box.

On cost-effectiveness
Patrick,
The two design ideas battling it out in the superinsulation arena right now — at least in North America — are Passivhaus and net-zero-energy. If we are going to achieve the carbon-reduction goals necessary to address global warming, something close to one of these standards must soon be adopted for all new homes.

Neither approach is cost-effective, however, because fossil fuel is still cheap. Until the cost of fossil fuel includes the costs associated with the environmental damage these fuels create when burned, we will continue to build houses based on cost-effectiveness calculations that assume energy is cheap.

Alice's Restaurant Massacree
First, let me say I've really enjoyed reading the discussions on PH standards at GBA.com (all apparently inspired by John Straube's now infamous November review of that same standard).

I'm not a P.E. I don't have a degree in architecture. And I don't build houses for a living. However, I am very interested in energy efficient construction, in how we can build or retrofit existing structures for the future (call it global warming, peak oil, peak energy, overpopulation, or whatever).

What's apparent to me is that there is a tremendous density of knowledgable and talented people at this forum. It's also apparent that written communication lacks the necessary body language and emotion that might otherwise come across in a personal setting. Humor turns sour, challenges turn aggressive, and rebuttals sometimes miss the mark.

What I'd really like to say is that the proponents of these methodologies (both Building Science Corporation AND The Passive House Institute) could resolve many of these debates with real numbers, with hard facts, with scanned documents and photocopies.

If we're going back to the '70s to look at the Saskatchewan House, why not go back a few more years and use the kind of evidence from Guthrie's infamous musical monologue? I'm talking "8 X 10 colour glossy pictures with circles and arrows and a paragraph on the back of each one" . . .

Not really. But modeling and calculations and assumptions only get us so far. Michael Blasnik asked for information that one is hard pressed to find on energy efficient construction. Where is the data showing actual energy usage? Where are the scanned documents showing monthly electrical bills? Where are the natural gas bills? Where are the spreadsheets showing the actual kilowatt hours and CCFs?

So much happens BEFORE construction, so little afterwards. So much foreplay, yet when the house is built, and the climax over, what then?

Enough with percentages and cost effectiveness and theoretical calculations! Let's agree to use facts and bring this discussion to a different level.

For one, I would challenge Katrina Klingenberg to post (on this website or http://www.passivehouse.us or other appropriate venue) the actual energy use of the existing US structures built to Passivhaus standards. The Smith House has > 6 years of actual data. Fairview I was finished in 2007. Surely there are utility bills available that cover a 12-month period?

I would challenge the same of John Straube of BSC. I've followed the evolution of the Westford House over the last couple of years. I've seen the improvements in building envelope and appliances and equipment. I've oogled the charts and laughed my way through Joseph Lstiburek's witty insights. Along the way I've learned one-heck-of-a-lot, but where is the actual energy consumption data? Where are the utility bill summaries? Where are the 8 x 10 glossies?

If it's like Joe says - "It's the Energy Stupid!" - then let's see the bottom line. Let the proponents post their actual energy usage whenever it's available and then even the laymen (and dummies like me) can sort through the facts. I know this is sometimes done, and I don't want to discredit any person or organization that has posted actuals, but it's rare and often difficult to find.

Thank you to BSC and PSI and GBA and the many scientists and builders that day-by-day continue to build the knowledge base around this important subject. I'm both humbled and excited to participate in the fray. As a complete outsider I don't have an ego or reputation to bruise. I can equally appreciate Wolfgang Feist's humorous and 'feisty' posts as well as John Straube's critical evaluation of the PH standard.

At the end of the day we can all agree that both groups and both men are spearheading efforts on their respective continents. And even way down here in 'fly-over' Arkansas I can see the light blazing from the torch that Katrina carries from that birthplace of the Lo-Cal House.

Carry on ladies and gentlemen, carry on!

And just in case I didn't add enough fuel to the fire, I would love to see more posts / discussions / arguements / models (but most of all, FACTS) regarding a key difference between the BSC and PH models. I speak of the difference between BSC's insulated sheathing model vs. the PHI double-stud OR I-beam wall. I don't think this one has been flushed out thoroughly.

However, I stand by my statement that we need more data, less calculations. The modeling software is very useful during the design phase, helps in the decision making process (HVAC sizing, fenestration choices, etc.). But there's no substitute for 12 months of data AFTER the house is occupied.

I don't think the Smith House provides the best example.

The Fairview House(s) and the Westford House(s) are both built for the low income housing sector. Likely they are occupied by standard working class families, not building scientists or energy efficiency geeks. I don't imagine they would sweat over HVAC setback temperatures or eight minute showers. Having historical energy usage data on these houses would be valuable to the wider community of designers and builders out there trying to make informed decisions on their upcoming projects.

show that even the worst performing Passive Houses used less heating energy than the "low energy" homes they are compared to. Obviously, the more data the better. However, the PHPP does seem to be accurate in predicting energy use.

What are the other energy modeling programs that we could use to compare to PHPP?

Keep it simple but do it don't talk about it.
The calculation for treated floor areas is something that has huge determination in PH on the final results calculated through PHPP. You can make a case for exclusion and inclusion for window/door reveals and cupboard spaces being a plant room or broom cupboard – it becomes a naming convention to get you out of an equation fix.
Similarly the climate data, window size, orientation. And just about anything else you care to include. What is important in PH is that designers should strive to attain the ‘Optimum’ through a common sense approach having first understood and hopefully trained as PassivHaus designers. A good PassivHaus is a kind of balancing act realized through considered mathematics.
Stuff cannot be resolved through finite mathematics alone. Common sense has to bear some relevance. If you go to the bedroom and ‘bonk’ yer wife during a summer’s evening, I would suggest that the increase in energy requires opening the window. But leave that window open for the whole night and look at affect it causes to the results generated in the PHPP.
The ethos of Passivhaus is a very good one – to reduce the demand for energy without adversely affecting people’s lifestyle cultures. How we achieve that is through utilizing the art of PassivHuas mathematics. From my own viewpoint there are no hard finite rules. E.G: If you achieve an airtightness of say [email protected] which I assure you is possible here in the UK, then you can maybe consider some items not reaching the strict PH targets.
If we adopt a better ideology towards conserving what we have we will survive into the future. So let’s be positive and try those methods of energy conservation that work and let’s not become too conformist to finite rules. Try out PHPP and you will see that there is scope for adventure. Optimize and Balance = PassivHaus.